For many years, rafter squares have been used in establishing the angular relationships of the cuts for the ends of members used for framing roofs. Such squares as used in the United States, Canada and England have used graduations in feet and inches and have often included tables which would permit determination of various angular relationships and lengths based upon a primary entry of length of rafters per foot of run. Frequently, these tables will have entries aligned with a foot and inch scale on the tongue or body which serves as the factor for introducing the value of rise into the equation. Such squares have proven extremely useful in framing roofs since the relationship between inches and feet is simple to establish.
Illustrative of squares of this type are those shown in the following U.S. Pat. Nos.: Howard 247,353 granted Sept. 20, 1881; Roberts 651,057 granted June 5, 1900; Nicholls 672,455 granted Apr. 23, 1901; Smith et al 691,192 granted Jan. 14, 1902; Caylor 1,196,519 granted Aug. 29, 1916; Bick 1,236,817 granted Aug. 14, 1917; Hill 1,241,976 granted Aug. 2, 1917; Walters 1,463,605 granted July 31, 1923; and Crandlemere 1,704,462 granted Mar. 5, 1929.
Although various metric value squares have been proposed and utilized, none have offered the flexibility and the ease of the angular determinations provided by some of the above-mentioned U.S. patents. Illustrative of metric squares are those shown in Swiss Pat. No. 299,404; British Pat. No. 1,253,680; and French Pat. No. 820,790.
As will be readily appreciated, the metre is a considerably larger unit of measure than the foot. As a result, attempting to utilize millimetres and full metres as the means for determining angular relationships presents a substantial problem from the standpoint of size. Abbreviating the length of the scale employed to less than a metre presents a problem from the standpoint of attempting to orient position determining points on the tongue and blade.
It is an object of the present invention to provide a novel rafter square utilizing metric scales and metric relationships to permit determination of various angular relationships and lengths of framing members and their cuts.
It is also an object to provide such a rafter square which is relatively compact and yet permits highly accurate establishment of such cuts, dimensions and angular relationships.
Another object is to provide such a rafter square including tables for conveniently determining lengths of the roof framing members for various values of rise per metre of run and for determining the included angles for side cuts.